In the past, artificial rocks have been made by a variety of processes.
Polyester figerglass has been employed in the past for producing artificial rocks but presents a problem in that of requiring a gel coat or barrier coat to be first sprayed in the mold. The polyester resin conventionally employed for structural strength requires fiberglass reinforcing due to the inherent brittleness of the polyester resin. Also low production is encountered limited to one or two parts per mold per day.
Plaster and concrete have also been employed but are of disadvantage in that it is too heavy for producing large specimens. Durability, weathering and resistance to cracking and chipping represent further problems. Production is also generally limited to one or two parts per mold per day.
A particular problem has been presented in molding artificial rocks. Such rocks may be made in solid form of one type of plastic or another but have been limited in variety of design because of the high cost of molding as well as requiring time for production of both the mold and the molded product. For landscaping purposes different sizes and types of artificial rocks are desirable and high mold costs and operation expenses may be limiting factors in the production of such rocks of different size and appearance to simulate a natural setting.
A further problem has been in the presentation of artifical rocks of durability, strength and hardness that can withstand the rigors of the environment wear and tear that might be occasioned. Such rocks if used in an outdoor setting must be able to withstand weathering over a period of time and substantial physical abuse by the public that may be encountered in their landscape or other type of setting in which they are employed.